<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Wait traits requirements</title>
<link rel="stylesheet" href="../../../../doc/src/boostbook.css" type="text/css">
<meta name="generator" content="DocBook XSL Stylesheets V1.79.1">
<link rel="home" href="../../boost_asio.html" title="Boost.Asio">
<link rel="up" href="../reference.html" title="Reference">
<link rel="prev" href="WaitHandler.html" title="Wait handler requirements">
<link rel="next" href="WriteHandler.html" title="Write handler requirements">
</head>
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
<table cellpadding="2" width="100%"><tr>
<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../boost.png"></td>
<td align="center"><a href="../../../../index.html">Home</a></td>
<td align="center"><a href="../../../../libs/libraries.htm">Libraries</a></td>
<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
<td align="center"><a href="../../../../more/index.htm">More</a></td>
</tr></table>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="WaitHandler.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../boost_asio.html"><img src="../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="WriteHandler.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a>
</div>
<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_asio.reference.WaitTraits"></a><a class="link" href="WaitTraits.html" title="Wait traits requirements">Wait traits requirements</a>
</h3></div></div></div>
<p>
        The <code class="computeroutput">basic_waitable_timer</code> template uses wait traits to allow
        programs to customize <code class="computeroutput">wait</code> and <code class="computeroutput">async_wait</code> behavior.
        [<span class="emphasis"><em>Note:</em></span> Possible uses of wait traits include:<br> — To
        enable timers based on non-realtime clocks.<br> — Determining how quickly
        wallclock-based timers respond to system time changes.<br> — Correcting for
        errors or rounding timeouts to boundaries.<br> — Preventing duration overflow.
        That is, a program may set a timer's expiry <code class="computeroutput">e</code> to be <code class="computeroutput">Clock::max()</code>
        (meaning never reached) or <code class="computeroutput">Clock::min()</code> (meaning always in the
        past). As a result, computing the duration until timer expiry as <code class="computeroutput">e
        - Clock::now()</code> may cause overflow. —<span class="emphasis"><em>end note</em></span>]
      </p>
<p>
        For a type <code class="computeroutput">Clock</code> meeting the <code class="computeroutput">Clock</code> requirements
        (C++Std [time.clock.req]), a type <code class="computeroutput">X</code> meets the <code class="computeroutput">WaitTraits</code>
        requirements if it satisfies the requirements listed below.
      </p>
<p>
        In the table below, <code class="computeroutput">t</code> denotes a (possibly const) value of type
        <code class="computeroutput">Clock::time_point</code>; and <code class="computeroutput">d</code> denotes a (possibly const)
        value of type <code class="computeroutput">Clock::duration</code>.
      </p>
<div class="table">
<a name="boost_asio.reference.WaitTraits.t0"></a><p class="title"><b>Table 36. WaitTraits requirements</b></p>
<div class="table-contents"><table class="table" summary="WaitTraits requirements">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
                <p>
                  expression
                </p>
              </th>
<th>
                <p>
                  return type
                </p>
              </th>
<th>
                <p>
                  assertion/note<br> pre/post-condition
                </p>
              </th>
</tr></thead>
<tbody>
<tr>
<td>
                <p>
                  <code class="computeroutput">X::to_wait_duration(d)</code>
                </p>
              </td>
<td>
                <p>
                  <code class="computeroutput">Clock::duration</code>
                </p>
              </td>
<td>
                <p>
                  Returns a <code class="computeroutput">Clock::duration</code> value to be used in a <code class="computeroutput">wait</code>
                  or <code class="computeroutput">async_wait</code> operation. [<span class="emphasis"><em>Note:</em></span>
                  The return value is typically representative of the duration <code class="computeroutput">d</code>.
                  —<span class="emphasis"><em>end note</em></span>]
                </p>
              </td>
</tr>
<tr>
<td>
                <p>
                  <code class="computeroutput">X::to_wait_duration(t)</code>
                </p>
              </td>
<td>
                <p>
                  <code class="computeroutput">Clock::duration</code>
                </p>
              </td>
<td>
                <p>
                  Returns a <code class="computeroutput">Clock::duration</code> value to be used in a <code class="computeroutput">wait</code>
                  or <code class="computeroutput">async_wait</code> operation. [<span class="emphasis"><em>Note:</em></span>
                  The return value is typically representative of the duration from
                  <code class="computeroutput">Clock::now()</code> until the time point <code class="computeroutput">t</code>.
                  —<span class="emphasis"><em>end note</em></span>]
                </p>
              </td>
</tr>
</tbody>
</table></div>
</div>
<br class="table-break">
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2003-2021 Christopher
      M. Kohlhoff<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div></td>
</tr></table>
<hr>
<div class="spirit-nav">
<a accesskey="p" href="WaitHandler.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../boost_asio.html"><img src="../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="WriteHandler.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a>
</div>
</body>
</html>
